The present invention relates to novel water soluble products derived from methylol phosphorous compounds and aminoalkyl phosphonic acid esters and their derivatives, to the processes of using these water soluble materials to produce flame retardant textile materials, and to the flame retardant textile materials so produced.
The practice of treating textile materials for flame retardance has assumed increasing importance with the adoption of federal, state and municipal legislation designed to protect the public from unreasonable hazards of flammable textile products. The technological difficulties in providing treated textile materials and the required standards are quite well known.
It has been shown by numerous workers in the field that compounds containing phosphorus are effective flame retardants for textiles. The major problem is how to bind such phosphorus compounds to the textiles substrates, so that the bound phosphorus compound will remain attached to the fabric after multiple launderings, without destroying the esthetic appeal of the treated fabric.
The fabrics which are of major commercial importance for flame retardant treatment are those containing cellulosic materials such as cotton or rayon and/or those containing polyester. A commercially satisfactory treatment for polyester/cotton blended fabrics containing significant amounts of polyester has not yet been developed.
Many classes of phosphorus compounds have been disclosed in the prior art for the purpose of affording flame retardant textiles. These include phosphoramides or phosphoramidates, phosphates, phosphonic and phosphoric acids, phosphonates and phosphonium compounds. The only chemical classes which have had any commercial success to date are the phosphonates and the phosphonium compounds.
The phosphonium compounds referred to above are tetrakis (hydroxymethyl)phosphonium salts, the best known of which is the chloride. Reeves and Guthrie in U.S. Pat. No. 2,809,941 used a solution of tetrakis(hydroxymethyl)phosphonium chloride, melamine-formaldehyde resin and urea to treat cotton fabrics by a pad-dry-cure method. This treatment and slight modifications of it have been used commercially to give cotton fabrics flame-retardance durable to multiple launderings. The treatment, however, causes high fabric strength losses and makes the fabrics too stiff to use except for certain areas such as industrial cotton work clothing and tent liners.
Reeves and Guthrie in their later-filed U.S. Pat. No. 2,772,188 disclosed an improved process for forming an insoluble polymer of tetrakis(hydroxymethyl)phosphonium chloride in cellulosic fabrics by what is known as a chemical cure. In water there was made a pre-polymer of tetrakis(hydroxymethyl)phosphonium chloride and either methylolmelamine or urea or phloroglucinol. This solution was padded onto cotton fabric. The fabric was dried and then treated with ammonia (chemical cure) to produce an insoluble polymer in and on the fabric. The fabric was fire retardant.
Coates in U.S. Pat. No. 2,983,623 improved on this process by using a chemical cure which consisted of treating impregnated fabric first with gaseous ammonia and then with aqueous NH.sub.3. Pre-condensates were made by refluxing tetrakis(hydroxymethyl)phosphonium chloride in water containing either urea, melamine, a urea and thiourea mixture, dicyandiamide or guanidine. Water solutions of the pre-condensate were padded onto cotton fabric. The fabric was dried and subsequently put first into a gaseous ammonia chamber and then into an aqueous solution of ammonia to form an insoluble polymer in and on the fabric. This fabric was flame-retardant. The particular process using a tetrakis(hyrdoxymethyl)phosphonium chloride-urea pre-condensate has become commercial and is known as the "Proban" process. It is adequate for cellulosic textiles, but is not satisfactory for polyester-cotton blend fabrics.
Coates and Chalkey in U.S. Pat. No. 3,236,676 further simplified the process by using tetrakis(hydroxymethyl)phosphonium salts (abbreviated THP salts) neutralized with a base such as NaOH to a pH between 3 and 9.5 instead of the tetrakis(hydroxymethyl)phosphonium chloride-urea precondensate. Fabric was padded with the neutralized THP salt, dried and given a heat cure sufficient to fix the THP salt on the fabric. Subsequently the fabric was treated with ammonia to form an insoluble polymer in and on the fabric.
Beninate et al. in U.S. Pat. No. 3,607,356 improved on this process by omitting the heat cure to fix the THP salt prior to the treatment with gaseous ammonia. They neutralized THP salt with a base such as NaOH to a pH of about 7.5 to 7.9 They called this neutralized product THPOH. In reality a solution of THP salt neutralized in this way consists mostly of tris(hydroxymethyl)phosphine (Reeves et al., Textile Chemist and Colorist 2, 283-285 (1970)). Cotton fabric was padded with and aqueous solution of this "THPOH" and dried to a moisture content of about the normal cotton moisture regain, or a little higher. This fabric was then subjected to an atmosphere of dry, gaseous ammonia to form an insoluble polymer in and on the fabric. They claimed this process would give flame-retardance not only to cellulosic fabrics and wool but also to polyester-cotton blends. This process has been commercialized and is adequate for cotton fabrics, but does not give adequate flame-retardance to a polyester-cotton blend containing more than 20% polyester.
LeBlanc and Gray (Textile Chemist and Colorist 3, 263-265 (1971)) did a study on the application of THPOH finish to polyester-cotton blends. They found that it is possible to give a minimum level of fire-retardance to blends which have no more than 12.5-25% polyester. Even at these levels of polyester, the treated fabrics were excessively stiffened by the treatment.
The phosphonate finishes which are currently in commercial usage are effective only on fabrics containing more than about 85% cotton. These finishes contain methylolated dimethyl phosphonopropionamide which is disclosed by the CibaGeigy Corporation in U.S. Pat. No. 3,374,292 and an oligomeric vinyl phosphonate called Fyrol 76 and discussed by the Stauffer Chemical Company in the Proceedings of the 1974 Symposium on Textile Flammability published by LeBlanc Research Corporation. The methylol phosphonopropionamide is co-applied to fabric with a melamine-based resin binder and given a thermal cure in order durably to fix the phosphonate to the substrate. The oligomeric vinyl compound is applied to fabric in conjunction with N-methylolacrylamide and a free radical initiator and the treated fabric is then given a thermal cure in order to co-polymerize the applied reactants in situ. A detailed description and the application of these two types of compounds to fabric may be found in the Proceedings of the 1974 Symposium on Textile Flammability published by the LeBlanc Research Corporation.
Ciba-Geigy Corporation has disclosed a developmental product, Pyrovatex 3762, for making polyester-cotton blends flame retardant (John Leddy and Rene Eckert, "Durable Flame Retardant Finishing of Cotton and Polyester-Cotton Blends," Proceedings of the 1973 Symposium on Textile Flammability, LeBlanc Research Corporation, East Greenwich, R.I.). From German Specification DOS No. 2,136,407 it appears the product, a "phosphonium oligomer" is a water-soluble self-condensation product of tetrakis(hydroxymethyl)phosphonium chloride. It can be applied to polyester-cotton blends by a pad-dry-cure-afterwash process. The padding solution contains the self-condensation product Pyrovatix 3762, a dimethylolmelamine, urea, a softener and a wetting agent. The Pyrovatex 3762 has a highly objectionable phosphine-type odor during fabric processing and the processed fabrics are very stiff.
In British Pat. No. 761,985, ammonia is condensed with a THP salt but the product is a water-insoluble polymeric solid and is employed to treat cellulosic material as an emulsion in water. Products based on this patent have not been commercialized.
In Chemical Abstracts, Vol. 79 (1973) 20256x there is abstracted German DOS No. 2,242,681 which self-condenses tetrakis(hydroxymethyl)phosphonium chloride to remove water and leave a polymer which, with urea, forms a dispersible material for addition to viscose spinning dopes. In Chemical Abstracts, Vol. 79 (1973) 20258z there is abstracted German DOS No. 2,242,682 wherein THPC is condensed with an amine such as dodecylamine in xylene to give a condensate. In Chemical Abstracts, Vol. 79 (1973) 93383w there is abstracted German DOS No. 2,255,113 wherein THPC is simultaneously reacted with ammonia and urea.
U.S. Pat. No. 3,772,068 discloses compounds containing phosphonium and phosphoramido-methyl groups for the treatment of polyester-cellulosic fabrics. This patent also discloses the co-application of phosphonium salts and dimethyl propionamide derivatives and resin binders for the treatment of polyester cellulosic blends. Similar products are also disclosed in U.S. Pat. No. 3,699,192. None of these treatments, however, is believed to be commercial.
Thus, while 50/50 or 65/35 polyester/cotton blend fabrics comprise about one-third of the total textile fabrics currently produced in the United States, at the present time there is no commercially available finish for flame retarding such polyester/cotton blends. One of the problems is that the polyester polymer fiber has no reactive groups on it such as the hydroxyl groups on the cellulose polymer. When the polyester content of a fabric approaches 50%, the number of available hydroxyl groups on the fabric is decreased to such an extent that it becomes difficult to attach flame retardant compounds to the fabric. While Pyrovatex 3762 has more reactive methylol groups per molecule than do THP salts, so that it can by polymerized with a resin such as dimethylolmelamine with a higher efficiency than THP salts, its disadvantages have been outlined hereinabove.